The present invention relates to a cross-coil instrument with a predefined characteristic as well as a method for giving the instrument such a characteristic. More particularly the invention relates to a cross-coil instrument with a highly linear characteristic or a characteristic with linearity with different constants in different areas of the scale.
Conventional instruments with a highly linear characteristic are manufactured with moving-coil instruments. This is disadvantageous because moving-coil instruments with a highly linear characteristic are expensive. Furthermore, the indicating device of a moving-coil instrument is limited in rotation, because wires are connected to the rotating device. Another drawback on moving-coil instruments is that the indicating device has to be light-weight. This makes the instrument sensitive to static electricity and makes it vulnerable to mechanical stress, which can change the calibration of the instrument.
Conventional cross-coil instruments are used for various measuring and display purpose. For instance, for process-indication, measuring the level of liquid or temperature as rudder angle-indicators or else as a voltmeter and an ammeter. A cross coil type instrument includes a movable permanent magnet around which a plurality of coils are cross-arranged. Currents based on a quantity to be measured pass through the coils, which generate a composite magnetic field. The movable permanent magnet having a needle is rotated due to the generated composite magnetic field. The known cross-coil moving magnet measuring instruments have a core, which is used as winding form and within which the moving magnets are rotable supported. From one end of the core an extension protrudes, in which the shaft of the moving magnet is positioned, the magnet receiving the indicating device, which is extended out of said extension. Although, such known cross-coil instruments are linear to some degree, they fail in applications, where highly linear and accurate display is required. In applications, where the angles of its deflexion are greater than 90°, the calibration in one quadrant of the instrument can counteract the calibration in other quadrants of the instruments. Such calibration problems can make it difficult to achieve linearity. In other applications it would be desirable to have a highly un-linear characteristic. That would be the case, when the instrument has to show low values with high resolution and higher values with a low resolution. There is no easy way to change the characteristic of the known cross-coil instrument.
It is therefore the object of the invention to provide a cross-coil instrument with a characteristic which can be predefined. Such an instrument would be capable to receive an electrical input value and visually display that value with a predefined angle of deflexion.